1. Field of Invention
The invention relates to a display apparatus and an optical device. More particularly, the invention relates to a projection apparatus and a light condensing module.
2. Description of Related Art
In general, when a projection apparatus is projecting an image, a light valve would convert an illumination beam into an image beam and reflect the image beam to a projection lens. After then, the image beam is projected onto a screen by the projection lens to form the image.
To let the illumination beam emitted from a light emitting device be uniformly incident onto the light valve, before the illumination beam entering the light valve, several prisms are disposed in front of the light valve in the conventional manner to average the optical path lengths to the light valve for the illumination beam entering at different positions of the prisms. In addition, a gap is reserved between these prisms so as to generate an effect of total reflection and the image beam from the light valve can propagate along a specific direction and transmit through the prisms and then reach to the projection lens. In this manner, the conventional projection apparatus generally needs a larger volume to dispose the prisms. When the developing trend for the projection apparatus is to have smaller volume and even further to be adapted in a portable or hand-held electronic device, it is one of essential issues to be solved by the manufacturers about how to reduce the volume of the projection apparatus.
U.S. Pat. No. 7,178,920 has disclosed a compact projection apparatus, which includes a light source, a condensing lens, a color wheel, a light integrator rod, a total internal reflection (TIR) device with a lens surface, a light valve, and a projection lens, wherein the total internal reflection device with a lens surface includes a first prism and a second prism. In addition, U.S. Pat. No. 7,483,216 has disclosed an optical module, in which one of the total internal reflection prisms has a curving surface. Further, U.S. Pat. No. 5,309,188 has also disclosed a projection apparatus.